One step in the fabrication of modem electronic devices is the formation of a conductor pattern over a substrate through photolithographic masking and etching. This step employs a photoresist coating over a metal layer which is selectively exposed to actinic light through a mask defining the desired conductor pattern. The photoresist film is developed so that it, in turn, constitutes a mask having openings defining the regions of the conductor to be etched.
One method of assembling integrated circuit devices is to support a number of them on a ceramic substrate to form an assembly known as a hybrid integrated circuit. It is sometimes advantageous to use an electrophoretic resist as the photoresist for patterning the metal conductor pattern on the substrate of a hybrid integrated circuit. An electrophoretic resist is typically an organic chemical, usually polymethylmethacrylate based, which is deposited on the metal coating by an electroplating process. Such resists offer advantages of line-line photolithographic definition as well as physical robustness. After masking and etching of the metal layer to form the conductor pattern, the electrophoretic mask must be removed using a photoresist stripping solvent.
As is set forth in application of T. Fang, Ser. No. 07/874,472, filed Apr. 13, 1992, now U.S. Pat. No. 5,236,552, granted Aug. 17, 1993, a photoresist stripping solvent or "stripper" must meet many different criteria. A developed electrophoretic resist is particularly difficult to strip if it is coated on the titanium surface. Since titanium-copper-titanium metal layers are often used as conductors on hybrid integrated circuits, effective stripping can be difficult. Tetramethylammonium hydroxide pentahydrate in a carrier of dimethyl sulfoxide has been found to be effective for this purpose and meets the other requirements for photoresist stripping solvents. Unfortunately, its stripping capacity is fairly low. That is, only about one hundred forty substrates having dimensions of 11.4.times.9.5 centimeters can be processed using one entire gallon of stripper before the stripper becomes ineffective. The stripping solvent would be much more commercially practical if its stripping capacity could be increased.